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The Life Aquatic in Flooded Fields

OSU fisheries ecologist Guillermo Giannico (right) and student Randy Colvin examine the fish and amphibians that take refuge in the flooded channels of grass-seed fields in the Willamette Valley. Photo: Lynn Ketchum

Heavy rains in winter can inundate grass fields in the Willamette Valley with surprising aquatic life. Ongoing research by Oregon State University and the U.S. Department of Agriculture has found that flooded grass fields offer winter refuge to many kinds of fish, amphibians, and other wildlife associated more commonly with streams than with fields.

Surveying flooded grass fields through several winters, the scientific team has identified 11 native fish species, including redside shiners, sticklebacks, speckled dace, and an occasional trout or Chinook salmon.

“The fish find food and shelter in these flooded backwaters, then they move back into the streams as winter floods recede,” said Guillermo Giannico, a fisheries ecologist with Oregon’s Agricultural Experiment Station and one of the researchers on the project.

“Flooded ditches, drainage channels, and remnant wetlands mark the valley’s memory of its old floodplain before the river was channeled into a single mainstem generations ago,” Giannico said.

Mark Mellbye, an OSU Extension Service agronomist, works with farmers as part of the project, assessing the effects of conservation practices such as planting wildlife buffers and maintaining vegetation in drainages and field borders. Many of these practices preserve water quality, and Mellbye has found relatively low concentrations of nutrients and suspended sediments in the field drainages. He credits local grass seed producers for their efforts at conservation and for opening their farms to this research. More than 25 farmers have given access to their fields to determine amounts of nutrients and sediment in their drainages and to pinpoint when and where fish are found.

Fish such as this young cutthroat trout seek food and shelter in flooded fields, then move back into streams as flood waters recede. Photo: Guillermo Giannico

Giannico and Mellbye have teamed up with USDA researchers, including Kathryn Boyer of the Natural Resources Conservation Service, to determine which species use the seasonal drainages and how grass seed farmers can provide good habitat for wildlife and still produce income from their fields.

In addition, the researchers are examining what these fish are eating.

“When we began our research, we thought it would be the terrestrial invertebrates that help decompose straw in the seed fields that would be washed into the drainages and eaten by the fish,” said Jeff Steiner, a USDA agronomist with the Agricultural Research Service. “As it turns out, the fish are mostly feeding on aquatic invertebrates from the slow-moving drainages near fields.”